W3C home > Mailing lists > Public > public-html@w3.org > June 2007

Re: fear of "invisible metadata"

From: Laura Carlson <laura.lee.carlson@gmail.com>
Date: Fri, 22 Jun 2007 17:34:51 -0500
Message-ID: <1c8dbcaa0706221534g2ababba0j9b9a270f902df5f6@mail.gmail.com>
To: public-html@w3.org

On 6/21/07, Maciej Stachowiak <mjs@apple.com> wrote:

> Not just "good", sometimes there's no alt text that could be added
> which would help accessibility, and yet it would be wrong to consider
> the image as purely decorative and semantically null. That's all I'm
> saying. There should be a way to mark up an image as being meaningful
> but having no alternative text.

I've found it useful to categorize non-text content into three levels:

1. Eye-candy:

 Eye- Candy are things that serve no purpose other than to make a site
visually appealing/attractive and (in many cases) satisfy the
marketing departments. There is no content value (though there may be
value to a sighted user). Never alt-ify eye-candy unless there is
something there which will enhance the usability of the site for
someone using a non-visual user agent. Use alt="" or CSS background
images instead.

2. Mood-Setting:

This is the middle layer of graphics which may serve to set the mood
or set the stage as it were. These graphics are not direct content and
may not be considered essential, but they are important in that they
help frame what is going on. Try to alt-ify the second group as makes
sense and is relevant. There may be times when doing so may be
annoying or detrimental to other users. Then try to avoid it. For
instance ALT text that is identical to an adjacent text is
unnecessary, and an irritant to screen reader users. I recommend
alt=""  or CSS Backgrounf images in such cases. But sometimes, it's
important to get this content in there for all users. Most times it
depends on context. The same image in a different context may need
drastically different alt text. Obviously, content should always be
fully available. The way you go in this case is a judgement call.

3. Content/Function:

This is where the image is the actual content. Always alt-ify content
and functional images. Title and long description attributes may also
be in order.

A way to check the usefulness of alternative text is to imagine
reading the page over the telephone to someone. What would you say
when encountering a particular image to make the page understandable
to the listener?

Besides the alt attribute you have a few more tools at your disposal
for images, like  title and longdesc attributes.

First, in degree of descriptiveness title is in between alt and
longdesc. It adds useful information and can add flavor. It helps
people who have screen readers set up to work with it. The title
attribute is optionally rendered by the user agent. Remember they are
invisible and not shown as a "tooltip" when focus is received via the
keyboard. (So much for device independence). So use the title
attribute only for advisory information. The fact that title attribute
happens to render as a tooltip for mouse users possibly deals with the
majority, but we are talking about providing the same equivalent
information for everyone.

Second, the longdesc attribute points to the URL of a full description
of an image. If the information contained in an image is important to
the meaning of the page (i.e. some important content would be lost if
the image was removed), a longer description than the "alt" attribute
can reasonably display should be used. It can provide for rich,
expressive documentation of a visual image. It should be used when alt
and title are insufficient to embody the visual qualities of an image.
As Joe Clark says in "Building Accessible Websites", "A longdesc is a
long description of an image...The aim is to use any length of
description necessary to impart the details of the graphic. It would
not be remiss to hope that a long description conjures an image - the
image - in the mind's eye, an analogy that holds true even for the
totally blind."

Something to keep in mind is that not all images need alternative
text, long descriptions, or titles. In many cases, you are better off
just going with your gut instinct -- if it's not necessary to include
it, and if you don't have a strong urge to do it, don't add that
longdesc. However, if it's necessary for the whole page to work, then
you need to add the alt text (or title or longdesc).

What's necessary and what's not depends a lot on the function of your
image and its context on the page. The same image may require alt text
(or title or longdesc) in one spot, but not in another. If an image
provides absolutely no content or functional information alt="" or CSS
background images may be appropriate to use. But if the image provides
content or adds functional information an alt would be required and
maybe even a long description would be in order. In many cases this
type of thing is a judgement call.

It's hard to come up with a general "best rule" for alt text, since in
many cases it's a matter of style. If you made a test of 10 different
images and asked 10 different accessibility "experts" to provide alt
text, you will likely get 10 different sets of answers.

The key, I think, is to cultivate the mindset whereby web authors take
alt text into consideration, and not necessarily insist on one
person's view of "the perfect alt text" for each image. In nearly
every case, it is better to have tried and put what YOU think is
appropriate -- based on your knowledge of assistive technology -- than
to attempt to please everyone with "the perfect answer."

In fact, you can get different answers from different blind folks as
well. If you are looking for perfection, you will fail, since you
won't be able to please all of the folks all of the time.

If you are looking for usability, however, that is fairly easily
accomplished and will provide heightened access to a huge number of
people who would be otherwise without.

It is good to consider what the "best" alt text is. It is more
important to have a "decent" alt text than to achieve a mythical
"perfect" one.

It comes down to using your judgement again.

This field of web accessibility is fascinating in that there are
countless intricacies and finer points. And sometimes there are no
clear cut answers.

Berst Regards,

[1] http://joeclark.org/book/sashay/serialization/Chapter06.html

Laura L. Carlson
Received on Friday, 22 June 2007 22:34:56 UTC

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